A human papovavirus, JCV, is the etiologic agent of the fatal demyelinating disease, progressive multifocal leukoencephalopathy. The JCV 98-base-pair tandem repeats, located to the late side of the viral replication origin, were shown to be a transcriptional regulatory element with enhancer-like activity in human fetal glial cells. These tandem repeats share significant homology with the 82-nucleotide rat brain-specific identifier RNA sequence.